1. Field of the Invention
The present invention relates to a high-frequency front end circuit that transmits and receives high-frequency signals.
2. Description of the Related Art
Various types of high-frequency front end circuits have been proposed thus far. Some high-frequency front end circuits include duplexers that combine a transmission filter and a reception filter, such as that disclosed in Japanese Unexamined Patent Application Publication No. 2004-120295.
In the duplexer, one end of the transmission filter and one end of the reception filter are connected in a common terminal configuration, and the common terminal is connected to an antenna or an antenna-side circuit. Another end of the transmission filter is connected to a transmission circuit, and another end of the reception filter is connected to a reception circuit.
According to such a high-frequency front end circuit, the transmission filter and the reception filter are connected, and thus to prevent a transmission signal from sneaking into the reception filter side, an impedance is set at the fundamental frequency of the transmission signal such that the reception filter side is open as seen from the transmission filter side.
However, it has been discovered that the reception sensitivity of the reception circuit connected to the reception filter will decay in such conventional high-frequency front end circuits even if isolation is ensured between the transmission filter and the reception filter as described above.